[Q] Slow/buggy/poor data connection and reception topic

I was originally a Verizon user so I'm not used to this kind of weak connection.
I had my phone replaced already due to another issue a few weeks ago
so I don't want to get another replacement because of this. it is really annoying!
Instead I will ask here and see if anyone could help !

**This has nothing to do with WiFi (because WiFi works great!)**
**And nothing to do with calls because call quality and connection showed no problems**
**Not exactly sure this problem started, just started getting annoyed with it recently**

\- What my phone is doing (when I'm at home) -/

1. Slow transition from WiFi connection
- When I turn Wifi off, I don't get an immediate data reception. Instead it takes about 10 seconds and then I barely start to get 3g..... not lte .... (It's not like this in every place)

2. Not much LTE
- It happens really rarely, most of the time at home the connection is on 3g :(

3. Lose data connection even while in use
- It's just sometimes unstable. When I'm browsing the web (while in 3g) it would sometimes go down to no bars at all and lose internet connectivity, then the 3g and I have to wait again until it comes back.
- Data roaming automatically turns on saying that I lost connection -_-

4. 3g is sometimes really unresponsive
- Just like when it is when turning off Wifi
- 3g would stay idle for sometime, even when I open apps that require internet
- Sometimes the 3g just disappears and decides not to comeback for a while

5. Bars up and down (drains battery?)
- I see this too often, like in every hour. While in 3g, the bars get suddenly full, then in an instant it drops to 1, then to 2. Then sometimes to no bars at all.
* in LTE it never gets like this, just constantly 1 bar

6. Maybe it's where I live?
- Possibly, but it's quite an urban and Sprint should have no problem covering this area in my opinion
- Verizon wasn't like this (although not perfect)

7. This is annoying
-Because it is draining the battery -_-
-Because my sister's iPhone 6 performs better (always has 2~3 bars) & my brother's S6 (though relatively weaker than her's) does not seem to lose connection compared mine at home (We're all Sprint users)


\- What I've done to confront this problem -/

1) Called Sprint, but didn't help at all. They told me to just take it to the store and have them take a look -__- Agent hardly knew anything...

2) Flashed Stock ROM and hard reset the phone (so annoying since you have to set things up again)

3) Made sure I set mobile data Network Mode to 'AUTOMATIC'

4) Made sure I have the latest Software version and have the PRL and Profile updated

But still no result at this point.


***Could this be a hardware issue? Or a software issue that is fixable?***

Can anyone give me some advice on how to fix this?

I mean it's just that the data reception is too weak an unreliable to think this is okay.

Right now my phone is pretty empty, barely any apps because of the reset.

I really don't want to believe it's due to a faulty hardware!

P.S. Possibly symptom?
The first day I got this phone as a replacement out of the store, I was unable to connect to the internet using data, even though calling was working.
What it was doing was, constantly switching from 3g - lte - inactive 3g - nothing - 3g - so on in a 20 second cycle.
By the end of that day towards midnight it was connecting to the internet.